Violet (Purple) Noise
Violet noise is known as differentiated white noise, due to its being the result of the differentiation of a white noise signal. Violet noise generates very high energies at higher frequencies. Its power density is proportional to f^2 and increases by 6 dB per octave.
Violet noise is also referred to as purple noise. These names come from visible light that turns into these colors when a similar spectral distribution is applied.
In other words...
Violet noise generates a lot of energy in the highest frequencies: each octave packs as much energy as the four octaves below it!
White noise, which is spectrally flat, seems already very bright for our auditory system. Violet noise will sound even brighter with the midrange and bass frequencies totally missing.
In audio applications, violet noise can be used for dithering, a process in which noise is intentionally applied to a signal in order to randomize quantization errors during bit depth conversions.
In healthcare applications, violet noise is used to mask tinnitus, a buzzing, ringing, or whistling in your ear, occurring without any stimulus.